James Hutton (left) and Joseph Black (right), natural philosophers, talking together. Etching and aquatint by J. Kay, 1787. https://www.rawpixel.com/image/14020923/image-cartoon-face-personFree Image from public domain licenseDavid Macbride. Engraving by J. T. Smith, 1797, after Reynolds of Dublin. https://www.rawpixel.com/image/14011742/david-macbride-engraving-smith-1797-after-reynolds-dublinFree Image from public domain licenseDavid Macbride. Engraving by J. T. Smith, 1797, after Reynolds of Dublin. https://www.rawpixel.com/image/13981518/david-macbride-engraving-smith-1797-after-reynolds-dublinFree Image from public domain license